Calamus (AOG-25) was launched 4 May 1944 by East Coast Shipyard, Inc., Bayonne, N.J., under a Maritime Commission contract; sponsored by Mrs. A. H. Moore; transferred to the Navy 7 July 1944; and commissioned the same day, Lieutenant W. Hord, USCGR, in command.

Calamus sailed from Norfolk 13 September 1944, bound for Pearl Harbor and Ulithi, where she arrived in mid-December and began her work as station tanker, fueling ships of the fleet as they brought the war ever closer to the Japanese homeland. Calamus cleared for Eniwetok 20 January 1945, and until February, pumped her vital gasoline into the ships readying there for the assault on Iwo Jima. Following the fleet she served westward, Calamus did station duty at Saipan from 11 February until 26 April, when she anchored off Okinawa to support the 3-week old assault. The tanker provided essential fueling service through the entire period of the island's assault and occupation, enduring the violent Japanese air attacks which marked the campaign as steadfastly as did the combatant ships.

Following occupation service, Calamus returned to San Francisco 20 March 1946. She was decommissioned 15 May 1946, and transferred to the Maritime Commission 4 September 1946.